1. Field of the Invention
The present invention relates generally to sealing gaskets and sealing systems used for pipe joints in plastic pipelines in which a male spigot pipe section is installed within a mating female socket pipe section to form a pipe joint, and to efforts to economize sealing systems for water, sewer agricultural and other fluid pipe sealing systems employing such pipe joints while maintaining acceptable pressure ratings.
2. Description of the Prior Art
Fluid sealing systems for plastic, fluid conveying pipes are used in a variety of industries. The pipes used in such systems are typically formed from thermoplastic materials including polyolefins and polyvinyl chloride (PVC). In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. Various types of sealing technologies have been employed to assure the sealing integrity of the pipe joint. It is important that the sealing gasket not be dislodged during the joint make up and that the gasket not become twisted or otherwise compromised in field applications.
One attempt to insure the integrity of the pipe joint involved the use of a pipe gasket having one region formed of an elastically yieldable sealing material, such as rubber, and a second distinct region formed of a more rigid material, such as a rigid plastic. Other approaches to the problem included the use of a homogeneous rubber ring with a stiffening band which was manually inserted into a mating groove provided on the internal diameter of the rubber ring. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing operation.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system provided an integral sealing mechanism within the belled or female pipe end for sealing with the spigot end of a mating pipe formed from thermoplastic material. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. The gasket was first positioned on the exterior of a cylindrical forming mandrel. The heated pipe end was forced over the forming mandrel and gasket. The female pipe end was then cooled and the forming mandrel was retracted, leaving the elastomeric gasket seated in an internal groove formed within the completed bell pipe end. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
Despite the advances offered by the Rieber process, difficulties were sometimes encountered in the belling operation, particularly with thin wall pipe. In some cases, the belling forces could rupture the thin wall pipe as the heated pipe end was forced over the belling mandrel and a traditionally sized elastomeric gasket seated on the mandrel.
There thus exists a need to provide a sealing gasket of reduced physical proportions for use in some belling operations, particularly those employing thin wall plastic pipe.
There also continues to exist the need to economize the sealing gasket and pipe joint manufacturing processes in order to produce gaskets in large quantities for use in countries worldwide at the lowest possible cost while maintaining an acceptable level of quality.
A need exists for a sealing gasket design which can be used in a Rieber type belling operation, which design provides optimum sealing capacity with the minimum amount of rubber being employed in order to provide a sealing gasket with a selective economy of scale.